Sealing units provided in bearing assemblies of railway axleboxes have to be designed such that they operate under very harsh conditions including temperature changes in a wide range, humidity and introducing dust or dirt from the outside while at the same time maintaining the sealing function and avoiding leakage of oil or grease out of the room accommodating the rollers of the bearings.
Hitherto, it was presumed that elastomeric seals are not suitable for applications requiring high robustness such as railway axlebox seals and that a friction contact would result in excessive wear in applications where dust may enter the contact surface.
The prior art therefore relied on felt rings or labyrinth seals.
Existing sealing units include seals which can be mounted directly on the bearing. However, this solution is available only for cylindrical roller bearings, tapered roller bearings or compact tapered roller bearings, because a special mechanic of the bearing is needed, which is not available for other types of bearings.
Further, it is known to provide a machined labyrinth-sealing between the backing ring and the housing or rear cover. This labyrinth can be positioned such that the parts engage with each other in an axial or radial direction. In principle, the small gap avoids most of the external intrusions. However, the efficiency of this sealing is directly linked to the size of the clearance inside the labyrinth. However, tolerances and permissible displacement must be considered so that the clearances have to be big enough to safely avoid collisions. The drawback of labyrinth seals besides of the high manufacturing costs is a feature that the labyrinth acts as a pump for the bearing grease which is moved outside the housing.
The traditional solution for the sealing is based on felt strips used in positions between the housing and the backing ring. This kind of sealing has a random efficiency depending on the wear and the environmental condition including temperature, ice, humidity etc. The purpose of the felt strip is to avoid the dust intrusion. However, in order to be efficient, it has to be protected by a labyrinth ring provided axially outside of the felt strip. The felt strip creates important friction which is reduced over the time, and experience shows that the service life of this component is not sufficient for most modern railway applications.